Question

A body is projected vertically upwards with a velocity u. It crosses a point in its journey at a height h twice, just after 1 and 7 s. The value of $\mu$ is ms-1 is: $(g=10{{m}^{-2}})$

• A. 50
• B. 40
• C. 30
• D. 20

Answer 1

Answer: (B)

40

Answer 2

The projectile of the body is shown in the figure. In the upward journey, the body is at A at t = 1 s and in downward journey it is at A at t = 7 s. Hence, we can conclude that during upward journey, the body will be at $\beta$ at t = 4 s.Thus, $v=u-gt$ $0=u-10\times 4$ $(\because \,v=0)$ $\therefore$ $u=40\,m/s.$